An imaging device, such as a digital still camera, includes an image sensor and generates image data based on the output data of the image sensor. Japanese Laid-Open Patent Publication Nos. 2011-164614 and 2010-081002 describe examples of the imaging device. The image sensor is, for example, a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). When capturing an image of a subject, light corresponding to the subject enters an image sensor through an optical system including a lens and the like. The image sensor generates output data in correspondence with the amount of incident light. An imaging device performs signal processing (e.g., color balance (or white balance) adjustment) on the output data of the image sensor to generate image data of the captured subject.
In an imaging device, the optical system includes a diaphragm. Poor adjustment of the diaphragm decreases the resolution of the image data obtained by the imaging device. Experience in diaphragm adjustment is necessary to limit decreases in the resolution.